The incorporation of bolt catch mechanism, such as in use with AR-15/M-16 type firearms is known in the art, one purpose for which being the ability to hold open a bolt or slide of a firearm firing mechanism in order to inspect the chamber after all rounds supplied by a magazine have been discharged. One known example of an ammunition magazine with internally supported and upwardly spring biased follower body is disclosed in Westrom, U.S. Pat. No. 5,638,626 and which discloses a bolt catch actuator coupled to the follower. The actuator is biasingly seated within the follower and further exhibits an actuation finger which, upon aligning the follower with a notch indicative of a last shot being fired, projects the finger through the notch in order to contact the bolt catch and restrain the reciprocating bolt in the open position.